Electronic devices use radio-frequency (RF) signals to communicate information. These radio-frequency signals enable users to talk with friends, download information, share pictures, remotely control household devices, receive global positioning information, employ radar for detection and tracking, or listen to radio stations. To generate these radio-frequency signals, an electronic device may include a clock generator, which generates a clock signal. The clock signal provides a stable frequency reference, which can be used to perform wireless communication. The clock signal may be provided, for example, to a mixer for frequency conversion (e.g., up-converting or down-converting communication signals) or a phase-locked loop for generating another signal having a different stable frequency reference.
Due to a reliance upon the clock signal, any frequency errors or noise in the clock signal can directly impact communication quality and performance. In some cases, operations performed using the clock signal may further increase a magnitude of the frequency errors or noise of the clock signal. As such, it is important that noise in the clock signal be within some predetermined threshold. One particular type of noise is phase noise, which represents random fluctuations in a phase of the clock signal. High levels of phase noise can raise an overall noise floor of a receiver, which decreases a sensitivity or a dynamic range of an electronic device. This makes it more challenging for the electronic device to detect weaker signals or signals that originate at farther distances.
Phase-noise performance of a clock generator can depend upon many factors, including power consumption and types of components. Better phase-noise performance is typically realized with higher power consumption or through utilizing larger size components. The former is expensive in terms of battery usage, and the latter is expensive in terms of device cost. Furthermore, different communication standards may be associated with different phase-noise thresholds. If an electronic device supports multiple communication standards (e.g., cellular, global positioning system (GPS), Wi-Fi, or Bluetooth™), a design of the clock generator may have to support more than one phase-noise threshold. Overall, it becomes challenging to design a clock generator that supports multiple communication standards, conserves power, and physically fits within a designated space.